It is well known that integrated circuits (ICs) are comprised of various electrical components fabricated in and on electronic substrates, such as silicon wafers, and may include metal oxide semiconductor (MOS) transistors, bipolar transistors, diodes, resistors, and capacitors. These components are connected to form electronic circuits by fabricating a series of vertical and horizontal metal interconnects, separated by dielectric materials, in the region above the components. The components generate heat when the integrated circuit is operated, requiring measures to be taken to dissipate this heat to avoid raising the temperature of the components in the integrated circuit above reliable operating temperatures, typically 100 to 130 degrees C. Heat dissipation measures, which may include heatsinks attached to the IC package or cooling fans blowing on the IC package, are typically configured to dissipate the heat generated by the IC and maintain the temperature of the components in the IC in a reliable operational temperature range, with a difference in temperature between the components in the integrated circuit and the external surface of the IC package in a range of 20 to 40 degrees C. Most of the heat generated by components in the IC is conducted mainly through the IC substrate, typically silicon, and through the interconnects over the components.
It is also well known that densities of components in integrated circuits are increasing with time, as articulated by Moore's Law, resulting in increasing power densities generated by the latest ICs. To maintain 20 to 40 degree C. temperature difference between the components in the integrated circuit and the external surface of the IC package, the thermal conductance of the elements in the IC package, including the IC itself, must increase with the increase in power dissipated by the circuits in the IC.
While the requirements for higher thermal conductance in the IC are increasing, two trends in interconnect fabrication are producing decreased thermal conductance through the interconnect region over the IC components. First, the number of interconnect levels is increasing over time, lengthening the thermal path between the IC components and the top surface of the IC. Second, the dielectric materials used to isolate the interconnect elements from each other are changing to less dense substances, in order to reduce capacitive coupling between circuit elements, which has a side effect of reduced thermal conductivity.